What tooth diff gear??

[Tobermory]

Hi all,
Just about to order a new Blackbone diff gear as mine is slipping when the engine mounts have been adjusted fully back Anyway im just wondering what tooth diff gear I should order I would like abit more top end so im presuming a smaller tooth gear would give me more top end??(Mine is a standerd 48 tooth) My layshaft gear is a 16 tooth btw.Also my engine is a stock 23cc with a jetpro clone and a 7500 rpm clutch spring.
Any advice would be appreciated
Thanks
Toby

 

[OuttaLuck]

24/38 combo would give you the maximum top end speed and 16/48 is the minimum bottom end speed


Pinion and spur gear combination 16/48 18/46 20/44 22/42 22/40 24/38


Troy

 

[Tobermory]

24/38 combo would give you the maximum top end speed and 16/48 is the minimum bottom end speed


Pinion and spur gear combination 16/48 18/46 20/44 22/42 22/40 24/38


Troy

Thanks for the reply Troy
So from reading that I'm guessing that the only gear I can run with the 16tooth spur gear would be the 48 tooth?? or is there any other gear that would mesh properly with the 16 tooth layshaft?? If not I'l have to go ahead and order the 48 tooth one.
Thanks
Toby

 

[hyper 78]

depends what youre doing.
the outside gears are easy to change so try changing them first.

the ratios given above are for the outside gears, pinion and spur, there is no exel ratio sheets for the inside gears.
you have a 16 layshaft gear so because the engine can be moved slightly you can use a 47 diff gear if you want. theres just enough movent in engine slots on the chassis to do so. probably give you another 3 or 4mph.

things that you will have to consider when choosing gears , 1) the wheels you use, very important, the size and weight of wheels. 2) engine and pipe youre using (power) 3) what gears you will use on the outside 'spur and pinion ' , 4) is the car 2wd or 4wd, 5) are you interested in more top speed or low end torque? without knowing all this its hard to say what diff gear to get

if youre using 18/46 outside and 16 lay then a 47 diff will be fine, might even be able to go to 46 diff but you might have to mod the diff brace a bit for the wider space between the diff gear and layshaft gear

im using a zen g270 and jetpro and the moment ive settled for 20/44 17/48 on grass , if i use slightly worn fg knobblies it has crazy bottom but if i use my new step studs then i get a second lag to come on pipe, although theres only 1 cm difference and 3 oz in weight ,there is a change to the performance,thats why tyre/ wheel choice is important too.on tarmac for speed runs i use 26/38 .ive also a 45 diff gear but need an 18 to go with it, the 45 is that small that you gotta get a bigger layshaft to fill the space between the gears

 

[Tobermory]

depends what youre doing.
the outside gears are easy to change so try changing them first.

the ratios given above are for the outside gears, pinion and spur, there is no exel ratio sheets for the inside gears.
you have a 16 layshaft gear so because the engine can be moved slightly you can use a 47 diff gear if you want. theres just enough movent in engine slots on the chassis to do so. probably give you another 3 or 4mph.

things that you will have to consider when choosing gears , 1) the wheels you use, very important, the size and weight of wheels. 2) engine and pipe youre using (power) 3) what gears you will use on the outside 'spur and pinion ' , 4) is the car 2wd or 4wd, 5) are you interested in more top speed or low end torque? without knowing all this its hard to say what diff gear to get

if youre using 18/46 outside and 16 lay then a 47 diff will be fine, might even be able to go to 46 diff but you might have to mod the diff brace a bit for the wider space between the diff gear and layshaft gear

im using a zen g270 and jetpro and the moment ive settled for 20/44 17/48 on grass , if i use slightly worn fg knobblies it has crazy bottom but if i use my new step studs then i get a second lag to come on pipe, although theres only 1 cm difference and 3 oz in weight ,there is a change to the performance,thats why tyre/ wheel choice is important too.on tarmac for speed runs i use 26/38 .ive also a 45 diff gear but need an 18 to go with it, the 45 is that small that you gotta get a bigger layshaft to fill the space between the gears

Thanks for the detailed reply Hyper!
Yeah the main reason i was asking what gear to buy was because mine is worn and I'm going to have to buy a new one,with a sped increse in mind i was just wondering if i could fit a different tooth gear to the diff as i am going to have to order one regardless.
However from reading your post i think im going to just order the 48 tooth stock one and maybe in the future change the outside gears to a different ratio when the need to be changed
Thanks
Toby

Sorry i forgot to ask Would there be a noticeable difference if i changed to a 47 tooth diff gear top speed wise?? also would i have to modify anything for it to fit?? Thanks

 

[hyper 78]

for a 47t diff you will probably see around 3 to 4mph, might not sound much but can make all the difference if your drag racing your mates. remember, its only one gear it shouldnt effect the bottom end.
if you changed the side gears from say 18/46 to 20/44 , thats just one up on the ratio but a total of 4 teeth difference.

the best thing to do if you can be bothered is unscrew the 4 engine bolts and the diff mount screw and see if the motor can be pushed back in the chassis slots toward the rear of the car , if so then the 47 will fit, im sure it will .they will have to sit slightly closer as the 47 is obviously smaller then a 48.
you can go back to a 48, and later change the outside gears.

 

[Tobermory]

for a 47t diff you will probably see around 3 to 4mph, might not sound much but can make all the difference if your drag racing your mates. remember, its only one gear it shouldnt effect the bottom end.
if you changed the side gears from say 18/46 to 20/44 , thats just one up on the ratio but a total of 4 teeth difference.

the best thing to do if you can be bothered is unscrew the 4 engine bolts and the diff mount screw and see if the motor can be pushed back in the chassis slots toward the rear of the car , if so then the 47 will fit, im sure it will .they will have to sit slightly closer as the 47 is obviously smaller then a 48.
you can go back to a 48, and later change the outside gears.

Right i think im going to order a 48 tooth one then,there is no body around my area that has a rc car that i would be racing and to be honest i don't think id really notice that small of an increase. Regarding adjusting the engine it is already as far back as it can go so i would have to start to modify the chassis to get it to go any further back and IMO it probably wouldn't be worth the hassle.
So im going to go ahead and order a 48 tooth one and possibly change the outside gears when they need replacing.
Thanks for all the replies!!
Toby